I do not remember who recommended a sound machine for us as we were planning on the birth of our first child; we registered for and received our beloved Marpac Sound Conditioner (affiliate link) which we have run nightly in the room of our older son. When my second son came along, we purchased another one and have been happily using it ever since. The devices seem to be unbreakable and provide uniform sound output. They are a bit bulky but the sound has less of the tinny quality of an electronic device . I have found it very useful when traveling as our older son especially is a light sleeper.
The principle behind the use of sound machines is the idea that constant sound prevents intermittent sounds (doors closing, siblings crying, etc) from interrupting sleep. For newborns, Dr. Harvey Karp popularized the idea that white noise louder than a baby’s crying replicated the sound in the womb and thus recommended white noise from a vacuum or loud “shushing” would help soothe a fussy baby (with my older son, this did seem to be true. You don’t know how loud you need to shush until you watch the video).
A recent study, however, has made me question the ongoing use of sound machines in our home. A group in Canada studied the amount of ambient noise generated by 14 infant sound machines (which were not identified by name). They used sophisticated techniques to measure sound levels; specifically, they used a sound booth and a device to simulate the size of an infant’s ear canal. They also corrected for the properties of the hearing of a six month old (thus, findings in the study are reported as A-weighted decibels, or dBA). They measured at three distances: 30 cm/ 11.8″ (as on a crib rail), 100 cm/ 39.4″ (as on a table next to the crib), and 200 cm/ 78.7″ (as if across the room). They found that:
1. All sound machines exceeded the maximum recommended sound exposures when placed on the crib rail.
2. Three machines produced volumes exceeding safe sound levels recommended for ADULTs (85 dBA) at the crib rail distance.
3. Although the sound levels were lower at the maximum distance, 13/14 machines generated levels greater than recommended volume (50 dBA) when at the loudest volume.
To put these findings in perspective, it is important to note that the recommend sound levels for infants in the hospital is quite low (50 dBA is quieter than normal conversation (60 dB) by about a factor of ten).
After reading this study, I wanted to measure the sound output from our sound machines to see how they compared. I used Cateater’s Sound Pressure Meter because I am powerless before a good looking app, but you can get a free app like Decibel 10th which will do the same thing for free.
The best number to use is the average as the max number is very sensitive to throat clearing, doors closing, or the laughter of your children “trying to be quiet while Daddy works”.The second and third distances represent the distances from the machines to the approximate head position of my sleeping 3 and 6 year olds.
I found that the sound levels were within safe limits for both of my boys (less than normal conversation), but they did exceed the very conservative limit for infants on the higher settings.
To give some perspective: normal conversation is 60 dB. For more on safe sound levels, the CDC has a good information page on safe sound levels and hearing loss in children.
So what should you do if you have been using a sound machine?
- Don’t panic! You likely have not done your child any harm. If you are worried about his or her hearing, your pediatrician can arrange screening. First off, moving your sound machine out of your child’s crib or bed is probably a good idea.
- It is probably a good idea to move your child’s sound machine out of their crib or bed and to the other side of the room.
- You can get a rough idea of how loud your device is by downloading a sound pressure meter application from your phone.
- You can also turn off your sound machine after your child goes to sleep. This is what we have started doing. Another option is to use a timer like this one which is what one of my colleagues who works in ENT does with his son.
- Don’t use the loudest volume settings if you can help it.
We have changed our practice by turning off the sound machines when we go to bed, although my six-year-old tends to get up and turn his back on. Did we do any permanent damage to our sons’ hearing when they were little? It is unclear, but I do not think so. (They don’t listen, but I don’t think that is due to their hearing).
Do you use sound machines for your children? If so, does this make you change your practice?